Iodine-131 is a radioactive isotope of iodine, commonly used in medical applications, particularly in the treatment of thyroid conditions. It emits beta and gamma radiation, which helps to destroy overactive thyroid tissue and is effective in treating certain types of thyroid cancer. This isotope has a half-life of about 8 days, meaning it takes that long for half of the substance to decay. Due to its relatively short half-life, iodine-131 is considered safe for medical use, as it minimizes prolonged exposure to radiation for patients undergoing treatment.